Derivative works are permitted under the MAME license. However, you are discouraged from providing specific functionality that goes against the philosophy of the MAME team. Specifically:
Do not add games which are more recent than 3 years old, or which are still being sold new by the company that produced them. MAME is not intended to be a platform that competes with arcade games that are still being actively sold.
Do not provide a means of generating a list of games that specifically identifies those games for which the user does not have image files. This only encourages users to seek out sources for illegal ROM, CD, and hard disk images in order to "complete" their collection.
Do not remove the startup screen that contains information about why certain non-working games don't work. This only serves to generate a bunch of useless email traffic to the developers asking why the games don't work.
Because the name MAME is trademarked, you must abide by the rules of the trademark usage if you wish to use "MAME" as part of the name your derivative work. In general, this means you must request permission, which requires that you follow the guidelines above.
The version number of any derivative work should reflect the version number of the MAME release it was derived from.
No license entanglements that I know of will change these wishes and continue to hope that people will respect the project and it's goal enough to comply.
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Re: What about nag screen rules?
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This nag screen rules
